The Coordinated Multipoint Transmission/Reception (CoMP) technology is adopted in a Long Term Evolution-Advance (LTE-A) system to lower interference from an adjacent cell to a User Equipment (UE) at the coverage edge of a cell and to improve an experience of the user equipment at the edge of the cell.
The coordinated multipoint transmission/reception technology refers to coordination between multiple transmission points which are separated geographically. Typically the multiple transmission points refer to base stations of different cells or a base station of a cell and multiple Remote Radio Heads (RRHs) controlled by the base station. The coordinated multipoint transmission/reception technology can be categorized into downlink coordinated transmission and uplink joint reception.
Downlink coordinated multipoint transmission is generally further categorized into two transmission schemes of Coordinated Scheduling/Coordinated Beam-forming (CS/CB) and Joint Processing (JP).
One of the multiple transmission points in CS/CB transmission transmits a useful signal to the user equipment, whereas the other transmission points lower interference to the user equipment through joint scheduling and beam-forming.
The JP scheme can be further categorized into Joint Transmission (JT) and Dynamic Point Selection (DPS). The multiple transmission points in JT transmit useful signals to the user equipment concurrently to thereby enhance received signals of the user equipment. A transmission point for the user equipment is switched dynamically in DPS transmission by always selecting from the coordinating transmission points the transmission point optimum for the user equipment to transmit signals to the user equipment. These coordinated multipoint transmission schemes can be used in combination. Also a Dynamic Blanking (DB) scheme may be combined with these coordinated multipoint transmission schemes, wherein some transmission points are configured, dynamically in some time-frequency resources, not to transmit any signal.
In order to support coordinated multipoint transmission/reception, the network configures one or more downlink reference signals for channel measurement, e.g., a Channel State Information-Reference Signal (CSI-RS). The user equipment can measure the downlink channel of each transmission point by using the downlink channel measurement reference signal configured by the network. The network can further configure one or more downlink reference signals for interference measurement, and the user equipment can measure interference under one or more interference assumptions by using the interference measurement downlink reference signal. The user equipment can obtain channel state information of each transmission point under the one or more interference assumptions from the measured downlink channels of the respective transmission points and interference under the respective interference assumptions. Under different interference assumptions, channel state information of a transmission point may include different Rank Indicators (RIs)/Pre-coding Matrix Indicators (PMIs) and Channel Quality Indicators (CQIs). In the process above, each transmission point corresponds to a reference signal resource possibly including one or more physical transmission points; and each interference assumption corresponds to an interference measurement reference signal resource.
After obtaining the channel state information, the user equipment reports the channel state information under the one or more interference assumptions according to the requirement for the transmission scheme. In the Long Term Evolution (LTE) system, two channel state information report schemes are supported, which are a periodical report based upon a Physical Uplink Control Channel (PUCCH) and a non-periodical report based upon a Physical Uplink Shared Channel (PUSCH) respectively.
The periodical report based upon a PUCCH includes report modes 1-0, 1-1, 2-0 and 2-1, wherein report modes 1-0 and 1-1 include broadband CQI information, and report modes 2-0 and 2-1 include user selected sub-band CQI information; and report modes 1-0 and 2-0 include no PMI information, and report modes 1-1 and 2-1 include PMI information. Furthermore, report mode 1-1 further includes sub-mode 1 and sub-mode 2 for transmission mode 9, wherein channel state information of 8 antenna ports of the base station is reported. The report modes above include all of report types 1, 1a, 2, 2a, 2b, 2c, 3, 4, 5 and 6, which are configured to report CQI, RI/PMI and Pre-coding Type Indicator (PTI) information, wherein report type 1 supports a user selected sub-band CQI report; report type 1a supports a user selected sub-band CQI and second PMI report; report types 2, 2b and 2c support a broadband CQI and PMI report; report type 2a supports a broadband PMI report; report type 3 supports an RI report; report type 4 supports a broadband CQI report; report type 5 supports an RI and broadband PMI report; and report type 6 supports an RI and RTI report.
The network configures report types of channel state information reports of each serving cell, a report periodicity and a sub-frame offset of a CQI/PMI report, and a report periodicity and a sub-frame offset of an RI report semi-statically through higher-layer signaling.
Different periodicities and sub-frame offsets may be configured between the different report types of each serving cell reported by the user equipment, and collision may occur in a channel information report process. When the collision occurs, the user equipment decides a report type according to the priorities of the report types and in the order of the numbers of the serving cells. Collision between report types includes: collision between report types at different priorities of the same serving cell, collision between report types at different priorities of different serving cells and collision between report types at the same priority of different serving cells. In collision between report types at different priorities of the same serving cell, the priorities of report type 3, 5 and 6 are higher than those of report types 1, 1a, 2, 2a, 2b, 2c and 4, wherein the report types at lower priorities are discarded. In collision between report types at different priorities of different serving cells, the priorities of report types 3, 5, 6 and 2a are higher than those of report types 1, 1a, 2, 2b, 2c and 4, wherein the report types at lower priorities are discarded. The network can further allocate a serving cell number to each serving cell, and in collision between report types at the same priority of different serving cells, report types of serving cells with higher numbers are discarded.
The non-periodical channel information report based a PUSCH includes report modes 1-2, 2-0, 2-2, 3-0 and 3-1, wherein report mode 1-2 includes broadband CQI information, report modes 2-0 and 2-2 include user selected sub-band CQI information, and report modes 3-0 and 3-1 include higher-layer configured sub-band CQI information; and report modes 2-0 and 3-0 include no PMI information, the report mode 3-1 report single information, and report modes 1-2 and 2-2 include multiple PMI information. The network configures a report mode for a non-periodical feedback of the user equipment semi-statically through higher-layer signaling. The network transmits DCI signaling to the user equipment over a Physical Downlink Control Channel (PDCCH) to trigger the non-periodical channel information report.
The inventors have identified during making of the present invention at least the following problem:
The existing periodical and non-periodical channel state information report methods are designed for a transmission scheme of a single transmission point for which only one report mode is configured, wherein report information in the report mode is based upon the same interference measurement so that it is impossible to support multiple transmission points for each of which channel state information under one or more interference assumptions is reported.